KR20140024398A - Method for producing water-absorbing resin - Google Patents

Abstract

The present invention is a novel process for producing a water absorbent resin by reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a petroleum hydrocarbon dispersion medium, wherein the water-soluble azo radical polymerization initiator is 0.00005 to 0.00016 mol per 1 mol of the water-soluble ethylenically unsaturated monomer. It provides a method characterized by performing a polymerization reaction in the presence of 0.000015-0.00015 mol hypophosphorous acid compound with respect to 1 mol of this water-soluble ethylenically unsaturated monomers. According to the method of the present invention, it is possible to control the release of the petroleum hydrocarbon dispersion medium to the outside of the reaction system to reduce the environmental load, and also to provide an absorbent resin that satisfies the characteristics of high water holding capacity, high water absorbing capacity under load, and low water content. You can get it.

Description

Method for producing absorbent resin {METHOD FOR PRODUCING WATER-ABSORBING RESIN}

The present invention relates to a method for producing a water absorbent resin and a water absorbent resin obtained thereby. More specifically, in the method for producing the water absorbent resin by reverse phase suspension polymerization, it is a manufacturing method that considers the load of the environment in which the release of the petroleum hydrocarbon dispersion medium to the outside of the reaction system is considered. It is related with the method of obtaining the water absorbing resin which satisfy | fills a characteristic, and has little water solubility, and the water absorbing resin obtained by it.

Absorbent resins are widely used in various fields such as sanitary materials such as paper diapers and sanitary products, agricultural horticultural materials such as water refining agents and soil improving agents, and industrial materials such as water repellents and anti-condensation agents. Among these fields, it is often used for sanitary materials, such as a paper diaper and a sanitary article.

As such a water absorbing resin, for example, a hydrolyzate of a starch-acrylonitrile graft copolymer, a neutralized product of a starch-acrylic acid graft copolymer, a saponified product of a vinyl acetate-acrylic acid ester copolymer, and a crosslinked product of an acrylic acid partial neutralized polymer Etc. are known.

These water absorbent resins are mainly manufactured by reverse phase suspension polymerization or aqueous solution polymerization of a water-soluble ethylenically unsaturated monomer. In these methods, in reverse phase suspension polymerization, since an organic solvent is used as the dispersion medium, it is necessary to consider the load on the environment such as the release of the organic solvent to the atmosphere, for example, high heat of polymerization or rapid In order to prevent release of the organic solvent by reaction, installation of an organic solvent recovery apparatus, etc. are required.

In addition, in a sanitary material such as a paper diaper, in addition to having a high water-retaining capacity as a desirable property of the water-absorbent resin, it has a high water-absorbing capacity under load in order to reduce the amount of return in the case where pressure is applied after absorption. Is required. In addition, in order to prevent adhesion of the viscous liquid to the skin, it is also an important condition that the water-soluble content is low. However, in the conventional manufacturing method of water absorbing resin, it is difficult to fully satisfy the balance of these characteristics.

In particular, the water holding capacity of the water absorbent resin and the water absorbing ability under load tend to be opposite. In general, in order to obtain high water-retaining capacity, it is necessary to lower the crosslinking density of the water absorbent resin. However, when the crosslinking density is lowered, the gel strength is lowered, and the absorbency under load is lowered. In addition, when the crosslinking density of the water absorbent resin is lowered, the uncrosslinked component is increased, and the water-soluble component is easily eluted when in contact with the liquid. As a result, when used in sanitary materials or the like, eczema due to the water-soluble component may be generated.

As a technique for improving the performance of a water absorbent resin, a method of performing reverse phase suspension polymerization using a specific amount of a specific surfactant (see Patent Document 1) and a method of performing reverse phase suspension polymerization in two or more stages (see Patent Document 2). ), A method of performing reverse phase suspension polymerization using a specific amount of persulfate as a polymerization initiator (see Patent Document 3), a method of using a water-soluble azo radical polymerization initiator in the presence of a specific internal crosslinking agent (see Patent Document 4), and the like. It is.

However, the water absorbent resin produced by the method described in Patent Documents 1 to 3 cannot fully satisfy all of the performances of high water retention capacity, high water absorption capacity under load, and low water content. In addition, in the reverse phase suspension polymerization described in the example of Patent Document 4, since the amount of the water-soluble azo radical polymerization initiator used is large, there is a problem that exothermic or abrupt reaction occurs and the organic solvent is released out of the reaction system. No load is considered.

Patent Document 1: Japanese Patent Laid-Open No. 6-345819 Patent Document 2: Japanese Unexamined Patent Publication No. 3-227301 Patent document 3: Unexamined-Japanese-Patent No. 6-287233 Patent Document 4: Japanese Patent Application Laid-Open No. 2006-176570

The present invention has been made in view of the above-described state of the art, and its main object is to reduce the environmental load by controlling the release of a petroleum hydrocarbon dispersion medium to the outside of the reaction system in a method for producing an absorbent resin by reverse phase suspension polymerization. The present invention provides a novel method for producing a water absorbent resin, and a water absorbent resin obtained thereby, wherein the water absorbent resin to be formed simultaneously satisfies the characteristics of high water holding capacity and high water absorbing ability under load, and further has low water content. .

The inventor of the present invention has conducted intensive studies in order to achieve the above object. As a result, when using a specific amount of water-soluble azo radical polymerization initiator as a polymerization initiator, and performing reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in presence of a specific amount of hypophosphorous acid compound, the organic solvent outside the reaction system In addition to being able to suppress the release of, it has been found that the water absorbent resin formed satisfies the characteristics of high water holding capacity, high water absorbing capacity under load, and low water content at the same time. Reached.

That is, this invention provides the manufacturing method of the following water absorbing resin, and the water absorbing resin obtained by it.

Item 1.A method for producing a water absorbent resin by reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a petroleum hydrocarbon dispersion medium, using 0.00005 to 0.00016 moles of a water-soluble azo radical polymerization initiator per 1 mole of the water-soluble ethylenically unsaturated monomer. And a polymerization reaction in the presence of 0.000015 to 0.00015 moles of hypophosphorous acid compound per 1 mole of the water-soluble ethylenically unsaturated monomer.

Item 2. The water-soluble azo radical polymerization initiator is 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- (1-(2-hydroxyethyl) -2- To item 1, which is at least one member selected from the group consisting of imidazoline-2-yl] propane} dihydrochloride and 2, 2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate The manufacturing method of the water absorbing resin described.

Item 3. The method for producing the water absorbent resin according to item 1 or 2, wherein the hypophosphorous compound is at least one member selected from the group consisting of hypophosphorous acid and sodium hypophosphite.

Item 4. The method for producing the water absorbent resin according to any one of Items 1 to 3, wherein the water-soluble ethylenically unsaturated monomer is at least one member selected from the group consisting of (meth) acrylic acid and salts thereof.

Item 5. The method for producing the water absorbent resin according to any one of Items 1 to 4, which performs reverse phase suspension polymerization in two or more stages.

Item 6. The method for producing the water absorbent resin according to any one of Items 1 to 5, wherein the crosslinking agent is added and post-crosslinked after completion of reverse phase suspension polymerization of the water-soluble ethylenically unsaturated monomer.

Item 7. Water absorbent resin obtained by the production method according to any one of Items 1 to 6.

Hereinafter, the manufacturing method of the water absorbing resin of this invention is demonstrated concretely.

Method for producing absorbent resin

The manufacturing method of the water absorbing resin of this invention is a method of reverse-phase suspension-polymerizing a water-soluble ethylenically unsaturated monomer in a petroleum hydrocarbon dispersion medium, using a specific amount of water-soluble azo radical polymerization initiator as a polymerization initiator, The specific amount of hypophosphorous acid compound It is a method characterized by performing a polymerization reaction in the presence of.

According to such a method, after using the specific amount of water-soluble azo radical polymerization initiator as a polymerization initiator to suppress release of the petroleum hydrocarbon dispersion medium outside the reaction system, the reverse phase suspension polymerization reaction can be stably performed. In addition, by using a specific amount of the hypophosphorous acid compound together with the water-soluble azo radical polymerization initiator described above, an absorbent resin having high water-retaining ability, high water-absorbing capacity under load, and low water-soluble content can be obtained simultaneously. .

Hereinafter, the manufacturing method of the water absorbing resin of this invention is demonstrated concretely.

(1) raw material compound

(Iii) water-soluble ethylenically unsaturated monomers

In the manufacturing method of this invention, a water-soluble ethylenically unsaturated monomer is used as a raw material. As the water-soluble ethylenically unsaturated monomer, for example, (meth) acrylic acid (in this specification, "acryl" and "methacryl" are collectively referred to as "(meth) acryl". The same applies hereinafter); 2- (meth) acrylamide-2-methylpropanesulfonic acid, salts thereof; Nonionic properties, such as (meth) acrylamide, N, N- dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, and polyethyleneglycol mono (meth) acrylate Monomers; Amino group-containing unsaturated monomers such as N, N-diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylamide, quaternary products thereof, and the like. It is available. These water-soluble ethylenically unsaturated monomers may be used independently and may be used in combination of 2 or more type.

Especially, since it is industrially easy to obtain, (meth) acrylic acid, its salt, (meth) acrylamide, N, N- dimethylacrylamide, etc. are preferable, and (meth) acrylic acid, its salt, etc. are more preferable. .

The above water-soluble ethylenically unsaturated monomer may be used as an aqueous solution in order to increase the dispersion efficiency in the petroleum hydrocarbon dispersion medium when performing reverse phase suspension polymerization. Although the density | concentration of the said monomer in such an aqueous solution is not specifically limited, Usually, what is necessary is just to be 20 mass% or more and saturation concentration or less, 25-70 mass% is preferable, and 30-55 mass% is more preferable.

When the water-soluble ethylenically unsaturated monomer has an acid group, such as (meth) acrylic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, etc., you may use the acid group previously neutralized by alkaline neutralizing agent as needed. Although it does not specifically limit as such alkaline neutralizing agent, For example, Alkali metal salts, such as sodium hydroxide and potassium hydroxide; Ammonia etc. are mentioned. In particular, these alkaline neutralizing agents may be used in the form of an aqueous solution in order to simplify the neutralization operation. Said alkaline neutralizing agent may be used independently and may be used in combination of 2 or more type.

The degree of neutralization of the water-soluble ethylenically unsaturated monomer by the alkaline neutralizing agent is not particularly limited, but by increasing the penetration pressure of the obtained water-absorbent resin, it is possible to increase the absorption capacity and to prevent problems such as safety due to the presence of excess alkaline neutralizing agent. In order to do so, it is good to set it as the range of 10-100 mol% normally as a degree of neutralization with respect to all the acidic groups which a water-soluble ethylenically unsaturated monomer has, and the range of 30-80 mol% is more preferable.

(Ii) petroleum hydrocarbon dispersion medium

As a petroleum hydrocarbon dispersion medium, For example, aliphatic hydrocarbons, such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2, 3- dimethylpentane, 3-ethylpentane, n-octane; Aliphatic hydrocarbons such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1, 2-dimethylcyclopentane, cis-1, 3-dimethylcyclopentane, trans-1 and 3-dimethylcyclopentane; Aromatic hydrocarbons, such as benzene, toluene, and xylene, etc. can be used. These petroleum hydrocarbon dispersion mediums may be used independently and may use 2 or more types together. Examples of the mixed hydrocarbon dispersion medium in which two or more petroleum hydrocarbon dispersion media are mixed include, for example, axle heptane (manufactured by Exxon Mobil, Inc., mixed hydrocarbon dispersion medium containing n-heptane, 2-methylhexane, 3-methylhexane, methylcyclohexane, etc.). ). Among these petroleum hydrocarbon dispersion mediums, n-hexane, n-heptane, cyclohexane, axole heptane and the like are preferable from the viewpoint of industrial availability, stable quality and low cost.

Although the usage-amount of a petroleum hydrocarbon dispersion medium is not specifically limited, In order to remove the heat of superposition | polymerization and to make it easy to control the reaction temperature of reverse phase suspension polymerization, it is usually made into 50-600 mass parts with respect to 100 mass parts of water-soluble ethylenically unsaturated monomers. It is good and 100-550 mass parts is more preferable.

(Iv) dispersion stabilizers

As a dispersion stabilizer used in reverse phase suspension polymerization, surfactant may be used. As the surfactant, for example, sucrose fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene Alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor oil, polyoxyethylene hardened castor oil, alkyl allyl formaldehyde condensation polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl Ether, polyethylene glycol fatty acid ester, alkyl glucoside, N-alkyl gluconamide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, phosphate ester of polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether Phosphate ester of le, etc. may be used. Among them, sorbitan fatty acid esters, polyglycerol fatty acid esters, sucrose fatty acid esters and the like are preferable from the viewpoint of dispersion stability of the aqueous monomer solution. These surfactant may be used independently and may use 2 or more types together.

The amount of the surfactant used is 0.1 to 5 with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer in order to maintain a good dispersion state of the water-soluble ethylenically unsaturated monomer in the petroleum hydrocarbon dispersion medium and to obtain a dispersion effect suitable for the amount used. A mass part, Preferably it is 0.2-3 mass parts.

Moreover, you may use together a polymeric type dispersion gel with surfactant as a dispersion stabilizer. Examples of the polymeric dispersant that can be used include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride-modified EPDM (ethylene propylene-diene terpolymer), maleic anhydride-modified polybutadiene, and anhydrous Maleic acid / ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, maleic anhydride / butadiene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidation Type ethylene propylene copolymer, ethylene acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose, etc. are mentioned. Among them, in view of the dispersion stability of the aqueous monomer solution, maleic anhydride modified polyethylene, maleic anhydride modified polypropylene, maleic anhydride modified ethylene / propylene copolymer, maleic anhydride / ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride, ethylene, Preferred are propylene copolymers, polyethylene, polypropylene, ethylene / propylene copolymers, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymers, and the like. These polymeric dispersants may be used independently and may use 2 or more types together.

The amount of the polymer-based dispersant is preferably based on 100 parts by mass of the water-soluble ethylenically unsaturated monomer in order to maintain a good dispersion state of the water-soluble ethylenically unsaturated monomer in the petroleum hydrocarbon dispersion medium and to obtain a dispersion effect suitable for the amount used. Is 0.1 to 5 parts by mass, more preferably 0.2 to 3 parts by mass.

(Iii) Water-soluble azo radical polymerization initiator

In this invention, it is necessary to use a water-soluble azo radical polymerization initiator as a polymerization initiator. As a water-soluble azo radical polymerization initiator, all the azo compounds which show water solubility in the state, or the azo compounds which show water solubility if it is neutralized and becomes a salt can be used.

By using such a water-soluble azo radical polymerization initiator within a specific amount of the range described later, the polymerization reaction can be stably progressed to obtain a water-absorbent resin with good performance, and also prevent rapid polymerization reaction to prevent petroleum hydrocarbon dispersion medium. The release to the reaction system outside of can be suppressed.

As a specific example of the water-soluble azo radical polymerization initiator which can be used by this invention, 1-{(1-cyano- 1-methylethyl) azo} formamide, 2, 2'- azobis [2- (N-phenyl ami) Dino) propane] dihydrochloride, 2, 2'-azobis {2- (N- (4-chlorophenyl) amidino] propane} dihydrochloride, 2, 2'-azobis {2- [N- (4- Hydroxyphenyl) amidino] propane} 2 hydrochloride, 2,2'-azobis [2- (N-benzylamidino) propane] hydrochloride, 2,2'-azobis [2- (N-allylamidino) ) Propane] dihydrochloride, 2, 2'-azobis (2-amidinopropane) dihydrochloride, 2, 2'-azobis {2--N- (2-hydroxyethyl) amidino] propane} dihydrochloride , 2,2'-azobis [2- (5-methyl-2-imidazoline-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazoline-2- (I) propane] dihydrochloride, 2, 2'-azobis [2- (4, 5, 6, 7-tetrahydro-1H-1, 3-diazepine-2-yl) propane ] Dihydrochloride, 2, 2'-azobis [2- (5-hydroxy-3, 4, 5, 6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2, 2'-azobis { 2-[1- (2-hydroxyethyl) -2-imidazoline-2-yl] propane} dihydrochloride, 2,2'-azobis [2- (2-imidazoline-2-yl) propane ], 2, 2'- azobis {2-methyl-N- [1, 1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2, 2'- azobis {2-methyl- N- [1,1-bis (hydroxymethyl) ethyl] propionamide}, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 2,2'-azo Bis (2-methylpropionamide) dihydrochloride, 4, 4'-azobis-4-cyanovaleric acid, 2, 2'-azobis [2- (hydroxymethyl) propionitrile], 2, 2 ' -Azobis [2- (2-imidazoline-2-yl) propane] disulfate dihydrate, 2,2'- azobis [N- (2-carboxyethyl) -2-methylpropionamidine] Azo compounds, such as a tetrahydrate and 2, 2'- azobis [2-methyl-N- (2-hydroxyethyl) propionamide], etc. Among these, 2, 2'- azobis (2-ami) is mentioned. Dinopropane) dihydrochloride, 2, 2'-azobis {2- (1- (2-hydroxyethyl) -2-imidazoline-2-yl] propane} dihydrochloride, 2, 2'-azobis [ N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate obtained the ease of adjustment of polymerization reactions, such as polymerization temperature, high water retention capacity, high water absorption capacity under load, and water-absorbent resin with few water solubility. It is preferable at that point. These water-soluble azo radical polymerization initiators may be used independently or may use 2 or more types together.

The amount of the water-soluble azo radical polymerization initiator to be used may be 0.00005 to 0.00016 mol with respect to 1 mol of the water-soluble ethylenically unsaturated monomer, and preferably 0.00007 to 0.00013 mol. When the amount of the initiator used exceeds the above range, a sudden polymerization reaction occurs and the petroleum hydrocarbon dispersion medium is easily released out of the reaction system, which is not preferable. On the other hand, when the amount of the initiator used is too small, it is not preferable because it takes a long time for the polymerization reaction, and the polymerization reaction becomes unstable and the polymer of the water-soluble ethylenically unsaturated monomer tends to be bulky.

(Iii) hypophosphite compounds

In the present invention, a water-repellent resin having high water holding capacity and high water absorbing capacity under load and low water-soluble content can be obtained by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in the presence of a specific amount of hypophosphorous acid compound described below.

Examples of the hypophosphite compound include hypophosphite, sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, barium hypophosphite, and ammonium hypophosphite. Among these, hypophosphorous acid and sodium hypophosphite are preferable from the point of obtaining industrially easy acquisition, high water holding capacity, high water absorption capacity under load, and low water solubility resin is obtained. These hypophosphorous acid compounds may be used independently or may use 2 or more types together.

The amount of the hypophosphorous acid compound used must be 0.000015 to 0.00015 moles per mole of the water-soluble ethylenically unsaturated monomer, and preferably 0.000025 to 0.00012 moles. When the usage-amount of hypophosphorous acid compound is too small, it is easy to be inferior to the water holding capacity of the water-absorbing resin obtained, and the water absorption capacity under load. On the other hand, when the usage-amount is too large, since the quantity of water-soluble content increases, it is unpreferable.

(Iii) internal crosslinking agent

In this invention, you may use a crosslinking agent as needed when carrying out reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer. Although it does not specifically limit as such a crosslinking agent (henceforth "internal crosslinking agent"), For example, the compound which has two or more polymerizable unsaturated groups can be used. As a specific example of such a compound, (poly) ethylene glycol (In this specification, "polyethylene glycol" and "ethylene glycol" are collectively represented as "(poly) ethylene glycol. It is the same hereafter.), (Poly Di or tri (meth) acrylic acid esters of polyols such as propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and (poly) glycerol; Unsaturated polyesters obtained by reacting the above-mentioned polyol with unsaturated acids such as maleic acid and fumaric acid; Bisacrylamides such as N, N'-methylenebis (meth) acrylamide; Di or tri (meth) acrylic acid esters obtained by reacting polyepoxide and (meth) acrylic acid; Di (meth) acrylic acid carbamyl esters obtained by reacting polyisocyanates such as triylene diisocyanate and hexamethylene diisocyanate with (meth) acrylic acid and hydroxyethyl; Allylated starch; Allylated cellulose; Diallyl phthalate; N, N ', N "-triallyl isocyanurate; Divinylbenzene and the like.

As an internal crosslinking agent, you may use the compound which has 2 or more of other reactive functional groups other than the compound which has 2 or more of said polymerizable unsaturated groups. As such an internal crosslinking agent, Glycidyl-group containing compounds, such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerine diglycidyl ether; (Poly) ethylene glycol, (poly) propylene glycol, (poly) glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, glycidyl (meth) acrylate, etc. can be illustrated. These internal crosslinking agents may be used independently and may be used in combination of 2 or more type.

In particular, since it is excellent in reactivity at low temperature, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerine diglycidyl ether, N, N'- Methylene bisacrylamide etc. are preferable.

Although an internal crosslinking agent may be added and used for a dispersion medium, in order to exhibit the effect by an internal crosslinking agent more efficiently, it is preferable to add to and use the said monomer.

When using an internal crosslinking agent, in order to fully raise the absorption performance of the water absorbing resin obtained, it is preferable to set it as 0.0000001-0.01 mol with respect to 1 mol of water-soluble ethylenically unsaturated monomers, and it is more preferable to set it as 0.000001-0.005 mol.

(2) reverse phase suspension polymerization method

In the present invention, in the presence of the specific amount of the hypophosphite compound in the petroleum hydrocarbon dispersion medium containing the dispersion stabilizer described above, the water-soluble ethylene is prepared by reverse phase suspension polymerization using the specific amount of the water-soluble azo radical polymerization initiator. What is necessary is just to superpose | polymerize a unsaturated unsaturated monomer. At this time, you may use the above-mentioned internal crosslinking agent as needed.

In the manufacturing method of the water absorbing resin which concerns on this invention, water of the quantity used as 10-200 mass parts with respect to 100 mass parts of said petroleum hydrocarbon solvents may be used. The amount of water to be used is preferably 10 parts by mass or more from the viewpoint of improving the dispersion state of the water-soluble ethylenically unsaturated monomer, from industrial viewpoints of favorable industrial production, and preferably from 200 parts by mass or less from the viewpoint of being economically preferable.

The reaction temperature of the polymerization reaction varies depending on the water-soluble azo radical polymerization initiator to be used. However, when the reaction temperature is too low, such as less than 20 ° C, the polymerization time becomes long, which is not preferable. On the other hand, in order to remove the heat of polymerization and to perform a smooth polymerization reaction, it is preferable that the upper limit of reaction temperature shall be 110 degreeC. From such a viewpoint, reaction temperature should just be 20-110 degreeC normally, and it is preferable to set it as 40-90 degreeC. The reaction time may be usually 0.1 hours to 4 hours.

In the present invention, the reverse phase suspension polymerization may be performed in one stage or in two or more stages. It is preferable that the number of stages is 2-3 stages from a viewpoint of raising productivity.

When performing two or more stages of reverse phase suspension polymerization, after performing the 1st stage reverse phase suspension polymerization, the water-soluble ethylenically unsaturated monomer is added and mixed with the reaction mixture obtained by the 1st stage polymerization reaction, and it is the same as that of 1st stage. What is necessary is just to perform reverse phase suspension polymerization of 2nd stage or more by the method. In reverse phase suspension polymerization in each stage after the second stage, in addition to the water-soluble ethylenically unsaturated monomer, a water-soluble azo radical polymerization initiator and a hypophosphite compound, and an internal crosslinking agent to be added as necessary, the reverse phase in each stage after the second stage. What is necessary is just to add in the range of the molar ratio of each component with respect to the said water-soluble ethylenically unsaturated monomer based on the quantity of the water-soluble ethylenically unsaturated monomer added at the time of suspension polymerization, and perform reverse phase suspension polymerization on the same conditions as the above-mentioned method.

(3) Fuga Bridge

In the present invention, in the step from the polymerization to the drying after the polymerization of the water-soluble ethylenically unsaturated monomer, the post-crosslinking treatment is performed by adding a postcrosslinking agent to increase the surface crosslinking density, and to increase the absorbent performance under load, such as hygiene and gel strength. A water absorbent resin suitable for the material can be obtained. As such a post-crosslinking agent, the compound which has two or more reactive functional groups is mentioned. Examples thereof include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerol; (Poly) ethylene glycol diglycidyl ether, (poly) ethylene glycol triglycidyl ether, (poly) glycerine diglycidyl ether, (poly) glycerine triglycidyl ether, (poly) propylene glycol polyglycidyl ether Polyglycidyl compounds such as (poly) glycerol polyglycidyl ether; Haloepoxy compounds such as epichlorohydrin, epibrohydrin, and α-methyl epichlorohydrin; Compounds having two or more reactive functional groups such as isocyanate compounds such as 2,4-trilene diisocyanate and hexamethylene diisocyanate; Oxetane compounds, such as 3-methyl-3 oxetane methanol, 3-ethyl-3 oxetane methanol, 3-butyl-3 oxetane methanol, and 3-methyl-3 oxetethanethanol, 1, 2- ethylene Carbonate compounds, such as oxazoline compounds, such as bisoxazoline, and ethylene carbonate, are mentioned. Among these, (poly) ethylene glycol diglycidyl ether, (poly) ethylene glycol triglycidyl ether, (poly) glycerine diglycidyl ether, (poly) glycerine triglycidyl ether, (poly) propylene glycol polyglycidyl Particularly preferred are polyglycidyl compounds such as dil ether and (poly) glycerol polyglycidyl ether. These postcrosslinking agents may be used independently and may use two or more types together.

The amount of the post-crosslinking agent added is 0.00005 mole to 1 mole of the total amount of the water-soluble ethylenically unsaturated monomer used in the reverse phase suspension polymerization reaction in order to increase the performance by increasing the crosslinking density near the surface without reducing the water absorbing ability of the obtained water absorbent resin. It is preferable to set it as the range of -0.01 mol, and it is more preferable to set it as the range of 0.0001 mol-0.005 mol.

Although the addition time of a post-crosslinking agent should just be after completion | finish of superposition | polymerization, it will not specifically limit, It is preferable to add in presence of water in the range of 1-400 mass parts with respect to 100 mass parts of solid content of a water absorbing resin, and it is moisture in the range of 5-200 mass parts. It is more preferable to add in presence, and it is most preferable to add in presence of water in the range of 10-100 mass parts.

When using a postcrosslinking agent, you may use water or a hydrophilic organic solvent as a solvent as needed. As a hydrophilic organic solvent, For example, lower alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol; Ketones such as acetone and methyl ethyl ketone; Ethers such as diethyl ether, dioxane and tetrahydrofuran; Amides such as N and N-dimethylformamide; And sulfoxides such as dimethyl sulfoxide. These hydrophilic organic solvents may be used independently and may use two or more types together. Moreover, you may use these hydrophilic organic solvents as a mixed solvent with water.

50-250 degreeC is preferable, as for the temperature in a post-crosslinking reaction, 60-180 degreeC is more preferable, 60-140 degreeC is still more preferable, 70-120 degreeC is especially preferable. Moreover, since the reaction time of the said post-crosslinking differs according to reaction temperature, the kind and quantity of a postcrosslinking agent, etc., it cannot determine uniformly, but is usually 1 to 30 minutes, Preferably it is 5 to 200 minutes.

(4) Drying

In the present invention, the drying step may be carried out under reduced pressure even under normal pressure, or may be carried out under air flow such as nitrogen in order to increase the drying efficiency. When a drying process is normal pressure, 70-250 degreeC is preferable, 80-180 degreeC is more preferable, 80-140 degreeC is more preferable, and 90-130 degreeC is especially preferable. Moreover, when it is under reduced pressure, 60-100 degreeC is preferable and, as for drying temperature, 70-90 degreeC is more preferable.

Absorbent resin

In order for the water absorbent resin obtained by the said method to have fluidity | liquidity after drying, the moisture content of the water absorbent resin after drying is 20% or less, It is more preferable that it is 1 to 15%, It is further more preferable that it is 3 to 10%. Moreover, you may add amorphous silica powder in order to improve fluidity.

When the water absorbent resin of the present invention is used in hygienic materials, it is preferable that it is 40 to 60 g / g, more preferably 40 to 50 g / g in order to increase the absorption capacity and reduce the amount of liquid return. desirable.

In addition, the physiological saline absorption capacity under 4.14 kPa load of the water absorbent resin of the present invention is preferably 15 ml / g or more in order to reduce the amount of reverse recovery when the sanitary material after absorption is under pressure when used in the sanitary material. It is more preferable that it is 20 ml / g or more.

The water-soluble component of the water absorbent resin of the present invention is preferably 20% by mass or less, more preferably 18% by mass or less in order to prevent adhesion of the viscous liquid with greasyness to the skin when used in hygienic materials.

As median particle diameter of the water absorbing resin suitable for an absorber and the absorbent article using the same, 200-600 micrometers is preferable, 250-550 micrometers is more preferable, 300-500 micrometers is more preferable.

In addition, the water content of the said water absorbing resin, the physiological saline water repair ability, the physiological saline water absorption capacity under 4.14 kPa load, an aqueous content, and the surrounding particle diameter are the values obtained by the measuring method as described in the Example mentioned later.

According to the method for producing the water absorbent resin of the present invention, the environmental load can be reduced by controlling the release of the petroleum hydrocarbon dispersion medium to the outside of the reaction system, and the water absorbent resin formed has high water holding capacity and high water absorbing capacity under load. It is said to have the outstanding characteristic that there is little melt. For this reason, the water absorbent resin obtained by the method of this invention can be used suitably for sanitary materials, such as a paper diaper, for example.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows schematic structure of the apparatus for measuring the absorption ability under a load.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited only to these Examples.

Moreover, about the water absorbing resin obtained by each Example and the comparative example, the water content, the physiological saline water retention capacity, the physiological saline water absorption capacity under 4.14 kPa load, the water content, and the median particle diameter were evaluated by the method shown below.

<Water content>

About 2 g of water-absorbent resin was precisely weighed into the aluminum wheel case 8 weighed in advance (Wa (g)). After drying the said sample with the hot air dryer (made by ADVANTEC company) which set internal temperature at 105 degreeC for 2 hours, it left to cool in a desiccator and measured the mass (Wb (g)) of the water absorbing resin after drying. The moisture content of the water absorbing resin was computed from the following formula.

Moisture content (mass%) = [Wa-Wb] / Wax 100

<Physiological saline water retention ability>

500 g of 0.9 mass% sodium chloride aqueous solution (physiological saline) was put into the 500 mL volume beaker, and 2.0 g of water absorbent resins were disperse | distributed so that agglomeration might not generate | occur | produce while stirring at 600 revolutions / min. It was left to stand for 30 minutes in the stirred state, and the water absorbing resin was fully swollen. Then, a dehydrator (made by a domestic centrifuge, product number: H) which poured into a cotton bag (cotton broad 60th, 100mm in width X 200mm in height), tied the upper part of a cotton bag with a rubber band, and set centrifugal force to be 167G. The cotton bag was dehydrated for 1 minute using -122), and the mass (Wc (g)) of the cotton bag including the swelling gel after dehydration was measured. The same operation was performed without adding a water absorbent resin, and the comass (Wd (g)) at the time of wet of the cotton bag was measured, and water retention capacity was computed from the following formula | equation.

Physiological saline water retention capacity (g / g) = [Wc-Wd] (g) / mass (g) of the absorbent resin

<Physiological saline absorption capacity under 4.14kPa load>

Physiological saline water absorption capacity under 4.14 kPa load of absorbent resin was measured using the measuring apparatus (X) which shows schematic structure in FIG.

The measuring apparatus X shown in FIG. 1 consists of the burette part 1, the conduit 2, the measuring stand 3, and the measuring part 4 put on the measuring stand 3. As shown in FIG. The burette part 1 has a rubber stopper 14 at the upper part of the burette 10, an air inlet pipe 11 and a cock 12 connected to the lower part, and an upper part of the air inlet pipe 11. 13) There is. A conduit 2 is attached from the burette 1 to the measuring table 3, and the diameter of the conduit 2 is 6 mm. In the center part of the measuring table 3, the hole of diameter 2mm is drilled, and the conduit 2 is connected. The measurement part 4 has the cylinder 40, the nylon mesh 41 adhere | attached on the bottom part of this cylinder 40, and the weight 42. As shown in FIG. The inner diameter of the cylinder 40 is 2.0 cm. The nylon mesh 41 is formed of 200 meshes (gap 75 mu m). Then, a predetermined amount of the water absorbent resin 5 is uniformly spread on the nylon mesh 41. The weight 42 is 1.9 cm in diameter and 119.6 g in mass. This weight 42 is placed on the water absorbent resin 5, and a load of 4.14 kPa can be uniformly applied to the water absorbent resin 5.

In the measuring apparatus X of such a structure, first, the cock 12 and the cock 13 of the burette part 1 are closed, and the physiological saline adjusted to 25 degreeC was put from the top of the burette 10, and the rubber stopper 14 After closing the upper part of the burette with), the cock 12 and the cock 13 of the burette part 1 are opened. Next, the height of the measuring stand 3 is adjusted so that the tip of the conduit 2 in the center of the measuring stand 3 and the air inlet of the air inlet pipe 11 are at the same height.

On the other hand, 0.10 g of the water absorbent resin 5 is uniformly spread on the nylon mesh 41 of the cylinder 40, and the weight 42 is placed on the water absorbent resin 5. The measurement part 4 makes the center part coincide with the conduit hole of the measurement stand 3 center part.

The amount of physiological saline absorbed in the burette 10 (the amount of physiological saline absorbed by the absorbent resin 5) (We (mL)) is continuously read at the time when the absorbent resin 5 starts to absorb. The physiological saline water absorption capacity under the load of the water absorbent resin 5 after 60 minutes from the start of absorption was calculated | required by the following formula.

Physiological saline absorption capacity (mL / g) under 4.14 kPa load

= We (mL) ÷ 0.10 (g)

<Solubles>

500 ± 0.1 g of physiological saline is placed in a 500 mL volume beaker, and a magnetic stirrer bar (without a ring of 8 mm ø x 30 mm) is placed and placed on a magnetic stirrer (product made by iuchi, product number: HS-30D). did. Subsequently, the magnetic stirrer bar was adjusted to rotate at 600 revolutions per minute, and the bottom of the vortex generated by the rotation of the magnetic stirrer bar was adjusted to be close to the top of the magnetic stirrer bar.

Next, 2.0 ± 0.002 g of the water absorbent resin was quickly poured into and dispersed between the vortex center in the beaker and the side of the beaker, and the mixture was stirred for 3 hours. The water-absorbent resin dispersion water after stirring for 3 hours was filtered through a standard sieve (gap 75 µm), and the obtained filtrate was suction filtered again using Kiriyama Roto (ADVANTEC Co., Filter Paper No. 6).

80 ± 0.0005 g of the filtrate obtained was weighed into a 100 mL volume beaker, which was dried, and dried to a constant volume with a hot air dryer (ADVANTEC Co., Model No .: FV-320) at 140 ° C, and the mass of the filtrate solid content (Wf ( g)) was measured.

On the other hand, it carried out similarly to the said operation, without using a water absorbing resin, measured the mass (Wg (g)) of filtrate solid content, and calculated the water-soluble content from the following formula.

Water-soluble fraction (mass%) = [(Wf-Wg) × (500/80)] / 2] × 100

<Median particle diameter>

0.25 g of amorphous silica (Degusa Japan Co., Ltd., Sipernat 200) was mixed with 50 g of water absorbent resin as a lubricant.

JIS standard sieve from above with a gap of 850 μm, gap of 600 μm, gap of 500 μm, gap of 425 μm, gap of 300 μm, gap of 250 μm, gap of 150 μm, and saucer The water-absorbent resin was added to the best sieve combined, followed by shaking for 20 minutes using a ro-tap shaker to classify.

After the classification, the mass of the water absorbent resin remaining on each sieve is calculated as a mass percentage of the total amount, and the cumulative value from the one with the larger particle diameter is accumulated in order to determine the relationship between the gap between the sieves and the integrated value of the mass percentage of the water absorbent resin remaining on the sieve. Plot on algebraic probability plots. The particle diameter corresponding to 50 mass% of integrated mass percentage was made into the median particle diameter by plotting the plot on the probability paper linearly.

Example 1

In a draft chamber, a round bottom cylindrical separable flask having a diameter of 110 mm and a volume of 2 L was prepared with a stirrer, a two-stage paddle blade, a reflux condenser (cooling part: allin cooler, length 60 cm), a dropping funnel and a nitrogen gas introduction tube. In addition, 5 degreeC cooling liquid was circulated to a cooling part using the cooling water circulation apparatus (EYELA COOL ACE CA-1112 by Tokyo Rikakikai Co., Ltd. product).

This flask was filled with 290 g of n-heptane, 0.74 g of sucrose stearic acid ester (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar ester S-370) and maleic anhydride-modified ethylene / propylene copolymer (Mitsui Chemical Co., Ltd., Hiwax 1105A). 0.74 g was added, it heated up to 80 degreeC, stirring, and dissolved surfactant, and cooled to 50 degreeC.

On the other hand, after filling 80 mass% of acrylic acid aqueous solution 92g (1.02 mol) in a 500 mL volumetric flask, 146.0 g of 21 mass% sodium hydroxide aqueous solutions were dripped while cooling from the outside, neutralization of 75 mol% was carried out, and the radical polymerization initiator 0.028 g (0.103 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride as an internal crosslinking agent, 0.010 g (0.0649 mmol) of N, N'-methylenebisacrylamide as an internal crosslinking agent, sodium hypophosphite as a hypophosphite compound -4.6 mg (0.0434 mmol) of hydrates were added and dissolved, and the monomer aqueous solution of the 1st stage was prepared.

After adding the entire amount of the aqueous monomer solution of the first stage to the separable flask to sufficiently replace the inside of the system with nitrogen, the flask was immersed in a 70 ° C. water bath to raise the temperature, and the polymerization of the first stage was performed for 30 minutes. The reaction mixture of the first stage was obtained.

On the other hand, 128.8 g (1.43 mol) of 80 mass% acrylic acid aqueous solution was filled in the 500 mL volume Erlenmeyer flask, 159.0 g of 27 mass% sodium hydroxide aqueous solutions were dripped, and it neutralized after 75 mol%, 0.039 g (0.144 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride as a radical polymerization initiator, 0.012 g (0.0778 mmol) of N, N'-methylenebisacrylamide, hypophosphorous acid compound as an internal crosslinking agent 6.4 mg (0.0608 mmol) of sodium hypophosphite-hydrates were added and dissolved to prepare a monomer aqueous solution of the second stage.

The reaction mixture of the first stage was cooled to 28 占 폚, the aqueous monomer solution of the second stage of the same temperature was added to the system, absorbed for 30 minutes, and the inside of the system was sufficiently substituted with nitrogen, and then the flask was 70 占 폚. It immersed in the water bath of and heated up, and superposed | polymerized in the 2nd step | paragraph was performed for 30 minutes. The n-heptane released to the outside of the flask at the time of reverse phase suspension polymerization reaction was collect | recovered by the trap at the reflux cooling part, and the mass was measured after completion | finish of polymerization, and the amount of n-heptane discharged out of the reaction system was 4.52g.

After the second stage of polymerization, the reaction mixture was heated up in an oil bath at 125 ° C, 248 g of water was taken out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water, followed by ethylene glycol diglycidyl ether. 4.42 g (0.51 mmol) of 2% aqueous solution was added, and the crosslinking reaction was performed at 80 degreeC for 2 hours. Thereafter, the reaction mixture was heated up in an oil bath at 125 ° C, n-heptane was evaporated and dried to obtain 230.5 g of a water absorbent resin. The median particle diameter of the water absorbent resin was 400 µm, and the moisture content was 5.1%. Table 1 shows the measurement results of each performance.

[Example 2]

In Example 1, 0.020 g (0.0737 mmol) of the 1st stage of the 2,2'- azobis (2-amidinopropane) dihydrochloride which is a radical polymerization initiator, and 0.028g (0.103) of the 2nd stage are used. Example 1, except that the amount of the first stage of the sodium hypophosphite-hydrate which is the hypophosphite compound was changed to 2.8 mg (0.0264 mmol) and that of the second stage was changed to 3.9 mg (0.0368 mmol). The same operation as the above was carried out to obtain 230.7 g of a water absorbent resin. The amount of n-heptane released out of the reaction system measured at the end of reverse phase suspension polymerization was 2.91 g. The median particle diameter of the water absorbent resin was 400 µm, and the moisture content was 6.0%. Table 1 shows the measurement results of each performance.

[Example 3]

In Example 1, 0.035 g (0.129 mmol) of the 1st stage of the 2,2'- azobis (2-amidinopropane) dihydrochloride which is a radical polymerization initiator, and 0.049g (0.18) of the 2nd stage are used. Millimolar), the amount of sodium hypophosphite-hydrate which is a hypophosphite compound is changed to 0.012 g (0.113 mmol) in the first stage, and 0.017 g (0.160 mmol) in the second stage, and the second stage is polymerized. The same operation as in Example 1 was carried out except that the amount of water taken out of the system after completion was changed to 241 g to obtain 231.8 g of a water absorbent resin. The amount of n-heptane released to the outside of the reaction system measured at the end of reverse phase suspension polymerization was 5.78 g. The median particle diameter of the water absorbent resin was 390 µm, and the moisture content was 5.8%. Table 1 shows the measurement results of each performance.

Example 4

In Example 1, the radical polymerization initiator was changed to 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate, and the usage amount of the first stage was 0.035 g (0.103). Millimolar), and the same operation as in Example 1 was carried out except that the amount of the second stage used was 0.049 g (0.143 mmol), to obtain 229.3 g of a water absorbent resin. The amount of n-heptane released to the outside of the reaction system measured at the end of reverse phase suspension polymerization was 5.53 g. The median particle diameter of the water absorbent resin was 410 µm, and the moisture content was 4.9%. Table 1 shows the measurement results of each performance.

[Example 5]

Example 1 WHEREIN: Except changing the hypophosphorous acid compound into hypophosphoric acid, the usage amount of the 1st stage was 3.7 mg (0.0561 mmol), and the usage amount of the 2nd stage was 5.2 mg (0.0788 mmol). The same operation as in Example 1 was performed to obtain 229.8 g of a water absorbent resin. The amount of n-heptane released to the outside of the reaction system measured at the end of reverse phase suspension polymerization was 4.38 g. The median particle diameter of the water absorbent resin was 400 µm, and the moisture content was 5.8%. Table 1 shows the measurement results of each performance.

Comparative Example 1

In Example 1, 9.2 mg (0.0339 mmol) of the 1st stage of 2,2'- azobis (2-amidinopropane) dihydrochloride which is a radical polymerization initiator, and 0.013 g (0.0479) of the 2nd stage of use were used. The same operation as in Example 1 was performed except for changing to millimolar). As a result, the polymerization reaction of the second stage was destabilized, and the polymer of the water-soluble ethylenically unsaturated monomer was agglomerated. The amount of n-heptane released to the outside of the reaction system measured at the end of reverse phase suspension polymerization was 2.16 g. About each performance, it could not be measured because of a block.

[Comparative Example 2]

In Example 1, 0.051 g (0.188 mmol) of the 1st stage of the 2,2'- azobis (2-amidinopropane) dihydrochloride which is a radical polymerization initiator, and 0.071g (0.262) of the 2nd stage are used. Except having been changed to (mmol), the same operation as in Example 1 was carried out to obtain 231.2 g of a water absorbent resin. The amount of n-heptane released to the outside of the reaction system measured at the end of reverse phase suspension polymerization was 9.59 g. The median particle diameter of the water absorbent resin was 380 µm, and the moisture content was 5.2%. Table 1 shows the measurement results of each performance.

[Comparative Example 3]

In Example 1, the amount of sodium hypophosphite-hydrate which is the hypophosphite compound is changed to 1.0 mg (0.0094 mmol) in the first stage, and the amount of the second stage is changed to 1.4 mg (0.0132 mmol) in the second stage, and the polymerization in the second stage is performed. The same operation as in Example 1 was carried out except that the amount of water drawn out of the system after completion was changed to 252 g to obtain 228.7 g of a water absorbent resin. The amount of n-heptane released to the outside of the reaction system measured at the end of reverse phase suspension polymerization was 4.65 g. The median particle diameter of the water absorbent resin was 400 µm, and the moisture content was 4.9%. Table 1 shows the measurement results of each performance.

[Comparative Example 4]

In Example 3, 0.041 g (0.151 mmol) of the 1st stage of the 2,2'- azobis (2-amidinopropane) dihydrochloride which is a radical polymerization initiator, and 0.058g (0.214) of the 2nd stage are used. Example 3, except that the amount of the first stage of the sodium hypophosphite-hydrate, which is a hypophosphite compound, was changed to 0.019 g (0.179 mmol) and the amount of the second stage was changed to 0.027 g (0.255 mmol). The same operation as the above was carried out to obtain 232.1 g of a water absorbent resin. The amount of n-heptane released to the outside of the reaction system measured at the end of reverse phase suspension polymerization was 7.48 g. The median particle diameter of the water absorbent resin was 420 µm, and the moisture content was 6.8%. Table 1 shows the measurement results of each performance.

[Comparative Example 5]

In Example 3, except that the radical polymerization initiator was changed to potassium persulfate, the amount used in the first stage was 0.028 g (0.104 mmol), and the amount used in the second stage was 0.039 g (0.144 mmol), The same operation as in Example 3 was performed to obtain 230.5 g of a water absorbent resin. The amount of n-heptane released out of the reaction system measured at the end of reverse phase suspension polymerization was 1.73 g. The median particle diameter of the water absorbent resin was 410 µm, and the moisture content was 5.2%. Table 1 shows the measurement results of each performance.

Radical polymerization initiator Hypophosphorous compound Emissions outside petroleum hydrocarbon dispersion medium reaction system Absorbent Resin Performance Kinds usage Kinds usage Physiological saline Physiological saline absorption capacity under 4.14kPa load Water soluble [Mole ^a) ] [Mole ^a) ] [Mass% ^b) ] [g / g] [mL / g] [mass%] Example 1 V-50 0.00010 Sodium hypophosphite 0.000043 1.6 46 24 13 Example 2 V-50 0.000072 Sodium hypophosphite 0.000026 1.0 48 20 12 Example 3 V-50 0.00013 Sodium hypophosphite 0.00011 2.0 46 26 18 Example 4 VA-057 0.00011 Sodium hypophosphite 0.000043 1.9 48 21 17 Example 5 V-50 0.00010 Hypophosphorous acid 0.000055 1.5 47 22 15 Comparative Example 1 V-50 0.000033 Sodium hypophosphite 0.000043 0.7 Inability to measure ^c) Comparative Example 2 V-50 0.00018 Sodium hypophosphite 0.000043 3.2 45 23 14 Comparative Example 3 V-50 0.00010 Sodium hypophosphite 0.0000092 1.6 46 11 12 Comparative Example 4 V-50 0.00015 Sodium hypophosphite 0.00018 2.8 46 23 45 Comparative Example 5 PPS 0.00010 Sodium hypophosphite 0.00011 0.6 48 13 24

a) It is about 1 mol of the water-soluble ethylenically unsaturated monomer used.

b) for petroleum hydrocarbon dispersion medium used for reverse phase suspension polymerization.

c) the monomer polymer is agglomerated.

<List of radical polymerization initiator abbreviations>

V-50: 2, 2'- azobis (2-amidinopropane) dihydrochloride

VA-057: 2, 2'-azobis (N- (2-carboxyethyl) -2-methylpropionamidine] 4

         Hydrate

PPS: Potassium Persulfate

As is apparent from Table 1, the production methods of Examples 1 to 5 are production methods in which the release of petroleum hydrocarbon dispersion medium to the outside of the reaction system is suppressed and the environmental load is considered, and also has high water holding capacity and high absorption capacity under load. Moreover, the water absorbent resin with little water solubility was obtained.

On the other hand, in the comparative example, when the usage-amount of a water-soluble azo radical polymerization initiator is small (comparative example 1), reverse phase suspension polymerization destabilized and the water-soluble ethylenically unsaturated monomer polymerized the mass. In addition, when the amount of water-soluble azo radical polymerization initiator used was large (Comparative Example 2), a water-absorbent resin having a high performance was obtained, but the amount of petroleum hydrocarbon dispersion medium outside the reaction system was large. In addition, when the amount of hypophosphorous compound used is small (Comparative Example 3), a water absorbent resin having low water absorption capacity under load is obtained. When the amount of hypophosphorous compound used is large (Comparative Example 4), a water absorbent resin having a large amount of water-soluble content is obtained. . Moreover, when persulfate was used as a radical initiator other than water-soluble azo radical polymerization initiator (comparative example 5), the water absorbing resin with low water absorption capacity under load was obtained.

X: measuring device
1: burette
10: burette
11: air inlet tube
12: cock
13: cock
14: rubber stopper
2: conduit
3: measuring table
4:
40: cylinder
41: nylon mesh
42: weight
5: absorbent resin

Claims (7)

As a manufacturing method of the water absorbing resin by reverse-phase suspension-polymerizing a water-soluble ethylenically unsaturated monomer in a petroleum hydrocarbon dispersion medium, it is water-soluble using 0.00005-0.00016 mol of water-soluble azo radical polymerization initiators with respect to 1 mol of this water-soluble ethylenically unsaturated monomers. A polymerization reaction is carried out in the presence of 0.000015 to 0.00015 moles of hypophosphorous acid compound per mole of ethylenically unsaturated monomer.
Way.
The method of claim 1,
The water-soluble azo radical polymerization initiator is 2,2'- azobis (2-amidinopropane) dihydrochloride, 2, 2'- azobis {2- (1-(2-hydroxyethyl) -2-imidazoline At least one member selected from the group consisting of-2-yl] propane} 2 hydrochloride and 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate.
Method for producing a water absorbent resin.
3. The method according to claim 1 or 2,
The hypophosphite compound is at least one member selected from the group consisting of hypophosphite and sodium hypophosphite
Method for producing a water absorbent resin.
4. The method according to any one of claims 1 to 3,
Water-soluble ethylenically unsaturated monomer is at least 1 sort (s) chosen from the group which consists of (meth) acrylic acid and its salt.
Method for producing a water absorbent resin.
5. The method according to any one of claims 1 to 4,
Performing reverse phase suspension polymerization in two or more stages
Method for producing a water absorbent resin.
The method according to any one of claims 1 to 5,
After completion of reverse phase suspension polymerization of the water-soluble ethylenically unsaturated monomer, a crosslinking agent is added to carry out postcrosslinking.
Method for producing a water absorbent resin.
Obtained by the manufacturing method in any one of Claims 1-6.
Absorbent resin.

Images